We suggest a method to determine the product of the coupling constants $g_{\\rho\\sigma\\gamma}g_
{\\sigma NN}$, in absolute value and relative sign, through the $t$-dependence of the two possible T-even asymmetries for the photoproduction of vector mesons, $\\gamma+p\\to p+V^0$, $V^0=\\rho$ or $\\omega$, in the collision of circularly polarized photons with a polarized proton target. In the framework of a $\\pi+\\sigma$-model, these asymmetries are very sensitive to the relative role of $\\pi$- and $\\sigma$-exchanges, in the near threshold region. |
